Polyurethane resin has remarkably been used in recent years for the sealing material, wall covering material, water proof material, coating or adhesive, because the polyurethane resin is excellent in various properties such as rubber elasticity, abrasion resistance, long service life etc.
The method for preparing the polyurethane resin is substantially classified into two groups, that is, one component method and two component method. In the one component method, terminal isocyanato radicals of polyurethane prepolymer cures by the atmospheric moisture. In the two component method, prepolymer containing principal component and polyol containing curing agent are mixed at the time of application to cause cure.
One component type polyurethane can be used by anybody because of its easiness in application method and has recently been attracted much attention in particular.
The one component type polyurethane is referred to as so called moisture curable polyurethane and the following compositions are already known in the art.
(1) Moisture curable polyurethane compositions by use of a reaction of polyisocyanate with moisture (water), that is, a reaction wherein a part of isocyanate converts to amine by the decarboxylation of isocyanate/water adduct and resultant amine reacts with another polyisocyanate molecule to carry out curing.
(2) Moisture curable polyurethane compositions composed of polyketimine and polyisocyanate (British Patent 1064841).
(3) Moisture curable polyurethane compositions composed of polyenamine and polyisocyanate (TOKKAISHO 57-16126 (1982)).
The compositions(1), however, have a relatively good storage stability in a sealed vessel whereas they have a markedly poor curing ability and a disadvantage of foaming. Amine or tin catalysts may be incorporated in order to improve the curing ability. These additives, however, have an adverse effect on the storage stability of the compositions, accelerate foaming and cause problems in actual use.
The compositions(2) are required to block the isocyanato radical in order to employ as the moisture curable polyurethane compositions, because polyketimine reacts with polyisocyanate. Besides the system consisting of blocked polyisocyanate and polyketimine has a characteristic of non-foaming whereas the system has a very low curing rate and causes troubles in actual application.
In the compositions(3), polyenamine also reacts with polyisocyanate. Therefore the same as in polyketimine, isocyanato radicals should be blocked when aromatic isocyanate is used as polyisocyanate, and lead to troubles in practical use. It has been known that polyenamine can be applied to sealing materials etc. in combination with polyisocyanate having relatively low activity, for example, aliphatic or alicyclic polyisocyanate. This system has characteristics of non-foaming and rapid cure. Polyenamine, however, reacts very gradually with aliphatic or alicyclic polyisocyanate and leads to poor stability in a long storage period or even in completely sealed containers at somewhat elevated temperatures. As a result, the initial physical properties of the sealing material cannot be maintained, the viscosity of the material is remarkably increased and causes a disadvantage of very poor workability. Therefore any of known prior arts has been unsatisfactory.
The above mentioned various problems are required to overcome industrially. That is, very important properties of such types of polyurethane are good storage stability in the sealed containers, high retention of the initial physical properties, prevention of gelation and good stability in viscosity. Curing rate must also be quick without foaming under atmospheric moisture. The value of commodity depends upon these properties.
In other words, a moisture curable polyurethane composition is strongly desired which is excellent in storage stability, capable of being stored for a long period under constant viscosity and also rapidly cured without foaming in the presence of moisture.